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Letter to Tesla – Large Drive Unit RMN failure

Dear Tesla, we have previously sent you a private letter, but this one is being made public on behalf of all Tesla owners and we know why your RMN LDU Fails. And sorry TESLA, but this time we have improved LDU to more power and more range. While conducting the EVC refurbishment process, we have observed degraded quality on REMAN drive units in 25 different instances.

When the drive unit was initially designed in early 2012, Tesla incorporated a slightly different rotor, superior wire winding isolation, and a more efficient thermal conductive epoxy. The coolant seal on the rotor was also better, and the only issue encountered at that time was milling pitch noise, which some early Tesla supporters may remember, and it was solely due to a single ball bearing made by SKF in India.

Subsequently, Tesla made design changes to certain components, but the most significant aspect is the quality of the critical parts, namely the rotor shaft seal and the stator. In the older Large Drive Units (LDUs) labeled with “P-TRAIN,” if the seal failed and coolant entered the unit, it didn’t cause irreparable damage to the stator windings. However, the new LDUs that were replaced under warranty suffered permanent damage upon any coolant ingress. We conducted several probe tests on local cars (in HR, SLO, AT) to explore different drying processes, but unfortunately, they were unsuccessful. Some cars experienced immediate failures, while others faced failures at a later stage, as depicted in the attached picture, where one phase winding almost exploded and caused a short circuit with the vehicle chassis.

We were particularly concerned about the situation that arose regarding the availability of used or new drive units. Our concern stems from the need to prioritize sustainability and repairability. The new drive units, which are priced at approximately 7000€, were not being sold to third-party workshops, raising questions about the accessibility and availability of these crucial components for repairs and maintenance.

Subsequently, we received a few drive units from Germany that had experienced significant coolant ingress, resulting in stator damage beyond repair. The isolation of these units fell below the threshold of 4.9 Mohm per drive unit or 16 MOhm per disconnected phase terminal. This situation further highlighted the importance of maintaining proper coolant sealing and ensuring the integrity of the stator to prevent such irreparable damage.

Out of the units we examined thoroughly, we discovered three pieces that were in a state of complete defect, leaving us with no viable options for repair. Through extensive research and analysis, we documented various failures in both RMN and P-TRAIN LDUs. Our findings revealed that RMN LDUs had a maximum lifespan of approximately 100,000 kilometers, while the older P-TRAIN LDUs were capable of lasting over 300,000 kilometers. The primary cause of failure in the new RMN LDUs was predominantly attributed to coolant seal issues. Additionally, we identified instances where the Reman facility had utilized a coolant seal with a single lip (it should have 3), which resulted in even faster deterioration of the LDUs (within 30,000 kilometers).

This 1002713-00-D coolant seal was with only 1 lip, and it failed on almost NEW RMN LDU from Italy.

It is important to highlight the experience of our friend Hansjörg Gemmingen, who reported having eight drive unit replacements within a mileage of 2 million kilometers. Interestingly, the first drive unit managed to last nearly 800,000 kilometers. This revelation left us puzzled 2 years ago, prompting us to delve deeper into understanding the reasons behind these variations and what we could anticipate as we embarked on research and development for the remanufacturing and lifetime repair of these complex and heavy LDU units. We must acknowledge that this project poses significant challenges due to its intricate nature and the high expectations of durability and longevity.

Repairing 100 battery packs with complex issues may seem easier compared to achieving sustainable quality and high mileage in repairing LDUs. The intricate nature of LDUs and the need for long-lasting performance make the repair process more challenging. Ensuring the drive unit reaches new high mileage requires meticulous attention to detail, quality control, and continuous improvements in the repair and remanufacturing processes. It is a demanding task that requires expertise and a commitment to delivering sustainable and reliable results.

During the initial stages of our research and development process, we conducted extensive testing by repeatedly removing, disassembling, and reassembling the drive unit approximately 16 times. This rigorous testing allowed us to evaluate the performance, durability, and reliability of the drive unit under various conditions. Through these iterative steps, we aimed to refine our repair and remanufacturing techniques to ensure optimal functionality and longevity of the drive units. We failed to repair 3 drive units completely and complexity was beyond imagination, and we know other 3rd party workshops failing too, even Tesla is failing to refurbish them.

And now we assembled that to “holy grail” opeartion manual eTraining at EVC Academy and we redesigned coolant seal issue and we redesigned, optimised and tuned stator winding.

Our new coolant system cant ever ever again let coolant inside stator.
Our new stator cant ever ever get low isolation or overheating problems
Our new stator should increase range and power, decrease heating of the system
Our complete LDU assembly should last at least 700000km

This process is not just repairing the stator winding but improving it significantly and it costs pretty much as high as 3000€ with Tax included, just to repair on part.

What Owners should do and how to prevent all of this happening:
1- If you got RMN label on LDU, it will fail at 100K. You should make preventive service on stator/rotor side.
2-If you got P-Train label and you just got pitch noise comming from it, you should make preventive service on stator/rotor side or complete reman.
3-If your RMN LDU failed, consider that you are buying even lower quality LDU from Tesla.

What Tesla Inc. should do:

1-Change coolant seal supplier
2-Change stator reman supplier
3-Redesign coolant drain after seal
4-Change isolation at winding wire
5-Change thermal conductive epoxy

This drive unit can be found in:
RWD S60 S70 S75 S85 S90 P85 P90
4×4 P85D P90D P100D

8 thoughts on “Letter to Tesla – Large Drive Unit RMN failure

  1. Hi, I’m from Poland and I have exactly that unit. My question is do you sell kit or something to make prevent fix?
    Regards Martin

    1. No we do not supply any kits or anything without proper training at EVC Academy. Anyone who tries to make successful reman on first attempt is a dreamer, he will fail expressly and we do not want to be part of that free fall.

  2. Hi EVClinic Team, Great work and insights, well done. Is it possible to get this upgrade at your shop, and if not for now, then when do you expect it to be available? Any idea about your price per drive unit? Br. Martin

  3. How have your tests gone with the newly designed motor?

    1. HI
      All tests passed, 5 pieces produced and assembled.

  4. I am a mechanical engineer student and I am dealing with a problem. Why the seals fail on a TESLA LDU (570A)? And what seals do you recommend to replace them? Kind regards

    1. 2-3 different problems with seal. Even if you use our seal, if you do not prepare 2 other problems, it will fail again. That info is our business secret and we do not share it publicly and for free.
      If LDU is RMN label on sticker, it is advised to make preventive repair of complete LDU to prevent complete failure.

  5. Vert good work!

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